1. Field of the Invention
This invention broadly relates to polymer systems used in converting processes, methods for their preparation, methods of using them and packages formed therewith. More particularly, it concerns new water borne, peroxy carbamyl group containing polymer systems, methods of forming them from polyurethane materials, and methods of using them, e.g., to make flexible packages from films, foils or like flexible sheet materials, particularly, retortable pouches and like flexible packages.
2. Description of the Prior Art
In the flexible packaging industry, many types of polymer systems are employed, e.g., adhesives, coatings, primers, binders, inks, etc. This invention provides new, improved polymer systems useable as adhesives, coatings, primers, binders, inks, or the like in converting or other processes.
A number of adhesive systems that are solvent-based and a select few water-based systems are being used in the production of laminates and other materials used in the packaging of food, non-food and medical products. While solvent-based adhesives have dominated this market for a number of years due to economical and ecological reasons, there is a growing need for competitive, high performance water borne adhesive systems.
Although a number of water-based adhesive systems claim to fulfill the various needs of the packaging industry, they all exhibit various disadvantages. This is due to the fact that the lamination process used in making packaging laminates, so-called converting, is complicated and involves many requirements for any acceptable adhesive system. Thus, useable adhesive systems should be machinable, compatible with a wide variety of printing inks, fast drying at very high coating speeds and devoid of foam or other undesirable problems. Further, the adhesive systems should be capable of bonding a host of different type films, paper products and foil to one another, yet provide very good initial and final bonding of such materials to give clear laminated end products. Depending on the product that packages made for such laminates are to hold, a number of other requirements must be addressed, e.g., retortable packages (see below) used for food or medical products should be able to withstand high retort temperatures and/or pressures.
A wide range of monolayer materials and multilayer structures are used in the flexible packaging industry for the containment of food, medical and other products. To meet the required compatibility of the packaging materials to the contents of the resulting packages, a variety of different flexible materials are used, e.g., papers, films, foils, metalized films and metalized papers. For the sake of brevity, all such materials will be referred to herein as flexiblele substrates. Also, the term flexible packages as used herein encompasses packages made entirely of flexible materials, e.g., pouches, as well as semirigid containers that lave at least one flexible body wall or lid.
One important class of flexible packages extensively used to contain food and medicinals are called retortable packages, i.e., packages capable of withstanding thermal processing in a pressure autoclave at temperatures in excess of 100.degree. C. (see "Retortable Flexible and Semirigid Packages", pps. 568-571, Willey Encyclopedia of Packaging Technology by Marilyn Bakker).
Retortable packages must maintain their material integrity as well as their required barrier properties during product-to-package handling, thermal processing and subsequent shipping and handling. In the case of shelf stable food packages, the flexible substrate used must be retortable and still maintain extended barrier characteristics. In making such retortable packages, flexible substrates have been sealed together by adhesives that are solvent-based systems. The processing of such adhesives takes a number of days, e.g., up to 13, to complete. In addition to this drawback, the solvent system adhesives present environmental and economic problems so there is an ever growing need for aqueous system adhesives capable of replacing solvent system adhesives. This invention helps to fulfill this need with new forms of polyurethane aqueous dispersions.
Aqueous polyurethane systems that are ionomeric in nature are a known class of product, see U.S. Pat. Nos. 4,598,121; 4,540,633 and 4,240,942, Canadian Pat. No. 837,176, German Pat. No. AS2624442 and references cited therein, the disclosures of which are incorporated herein by reference for their teachings concerning formation of polyurethane prepolymers that are converted into an ionomer containing free NCO groups which are then reacted with a diol or other difunctional reagent to give chain extended polymers. This invention uses this known prior art with a new combination of reagents to produce new forms of polyurethane aqueous dispersions that have been discovered to possess unique adhesive properties.